In a lithography process of manufacturing electronic devices (microdevices) such as semiconductor devices and liquid crystal display elements, a projection exposure apparatus of a step-and-repeat method (a so-called stepper), and a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner)) are mainly used. In these exposure apparatuses, illumination light is projected on a wafer (or a glass plate or the like) coated with photosensitive agent (resist) via a reticle (or a mask) and a projection optical system, and thereby (a reduced image of) a pattern formed on the reticle is sequentially transferred to a plurality of shot areas on the wafer.
Due to the finer pattern accompanying the higher integration of semiconductor devices in recent years, position control of a wafer stage with high accuracy has been required. Therefore, instead of a conventional position measurement system configured using a laser interferometer, a position measurement system configured using an encoder having a measurement resolution of a same level as or a higher level than the laser interferometer and a surface position sensor has come to be employed. For example, an encoder system and a surface position sensor system, which are employed in an exposure apparatus disclosed in PTL 1, project measurement beams on (a reflection type diffraction grating configuring) a measurement surface provided on a wafer stage, detect reflection beams of the measurement beams, and thereby measure the displacement in a periodic direction of the diffraction grating or the surface position (the position in a Z-axis direction) of the measurement surface (i.e., the wafer stage).
In order to raise the positioning accuracy of a wafer as well as improving the throughput, a planar motor that two-dimensionally drives a wafer stage that moves holding the wafer, e.g., a planar motor structured by coupling, for two axes, a linear pulse motor of a variable reluctance driving method that is capable of driving the wafer stage in a noncontact manner, a planar motor by the Lorentz electromagnetic force driving made by expanding a liner motor in two-dimensional directions (e.g., PTL 2), and further, a planar motor made of layering armature coils arrayed in one direction of two-dimensional directions and armature coils arrayed in the other direction of the two-dimensional directions (e.g., PTL 3 and PTL 4) have been developed.
In the case of a planar motor of a magnetic levitation method, a driving point on which a driving force acts (a bottom part of the wafer stage on which a mover is provided) is spaced apart from the center of gravity of the wafer stage. Therefore, in the case where the wafer stage goes out of control during the driving of the wafer stage, if the wafer stage is stopped by, for example, applying a dynamic brake on the wafer stage or causing the wafer stage to collide against a shock absorber or the like, then the pitching (the rotation tilted forward) is generated due to an inertial force, which may cause the upper surface (a wafer table) of the wafer stage to collide against a structure placed immediately above the upper surface and to suffer damage. In particular, in the encoder system and the surface position sensor system referred to above, the encoder (heads) and the surface position sensor (heads) that configure the systems are placed at the height of around 1 mm or more from the upper surface of the wafer stage. Further, in an exposure apparatus of a liquid immersion exposure method that exposes a wafer by irradiating illumination light via a projection optical system and liquid in a liquid immersion space (e.g., PTL 5), a liquid immersion device such as a nozzle that supplies immersion liquid to the liquid immersion space between the projection optical system and the wafer is placed immediately above the wafer stage.